Stability analysis of H-mode pedestal and edge localized modes in a Joint European Torus power scan

Abstract

Simulations of three Joint European Torus [P. H. Rebut et al., Nucl. Fusion 25, 1011 (1985)] type I ELMy high-confinement discharges in a power scan are carried out using the JETTO integrated modeling code [M. Erba et al., Plasma Phys. Controlled Fusion 39, 261 (1997)] with predictive core and pedestal models, which include the effect of edge localized modes (ELMs). It is found that current-driven peeling modes trigger the ELM crashes in these discharges and, as a result, yield an explanation of the experimentally observed increase in pedestal height with heating power. After each ELM crash, the pressure gradient and the related bootstrap current density at the edge of plasma rapidly increase with increasing heating power, while the total current density rises only slowly because the total current density is impeded by a back electromotive force. Hence, as the heating power is increased, the pedestal pressure can rise to higher values during an ELM cycle before the current density reaches the level required for destabilization of the current-driven peeling modes. In addition, a stability analysis using the HELENA and MISHKA codes [A. B. Mikhailovskii et al., Plasma Phys. Rep. 23, 713 (1997)] is carried out in conjunction with these simulations. The analysis includes infinite-n ideal ballooning, finite-n ballooning, and low-n kink/peeling modes.